Winter- and summertime continental influences on tropospheric O3 and CO observed by TES over the western North Atlantic OceanJ. Hegarty, H. Mao, and R. TalbotInstitute for the Study of Earth, Oceans and Space Climate Change Research Center University of New Hampshire, Durham, New Hampshire 03824, USA

Abstract. The distributions of tropospheric ozone (O3) and carbon monoxide (CO),
and the synoptic factors regulating these distributions over the western
North Atlantic Ocean during winter and summer were investigated using
profile retrievals from the Tropospheric Emission Spectrometer (TES) for
2004–2006. Seasonal composites of TES retrievals, reprocessed to remove
the influence of the a priori on geographical and seasonal structure,
exhibited strong seasonal differences. At the 681 hPa level during winter
months of December, January and February (DJF) the composite O3 mixing
ratios were uniformly low (~45 ppbv), but continental export was
evident in a channel of enhanced CO (100–110 ppbv) flowing eastward from
the US coast. In summer months June, July, and August (JJA) O3 mixing
ratios were variable (45–65 ppbv) and generally higher due to increased
photochemical production. The summer distribution also featured a channel of
enhanced CO (95–105 ppbv) flowing northeastward around an anticyclone and
exiting the continent over the Canadian Maritimes around 50° N. Offshore
O3-CO slopes were generally 0.15–0.20 mol mol−1 in JJA, indicative
of photochemical O3 production. Composites for 4 predominant synoptic
patterns or map types in DJF suggested that export to the lower free
troposphere (681 hPa level) was enhanced by the warm conveyor belt airstream
of mid-latitude cyclones while stratospheric intrusions increased TES
O3 levels at 316 hPa. A major finding in the DJF data was that offshore
681 hPa CO mixing ratios behind cold fronts could be enhanced up to >150
ppbv likely by lofting from the surface via shallow convection resulting
from rapid destabilization of cold air flowing over much warmer ocean
waters. In JJA composites for 3 map types showed that the general export
pattern of the seasonal composites was associated with a synoptic pattern
featuring the Bermuda High. However, weak cyclones and frontal troughs could
enhance offshore 681 hPa CO mixing ratios to >110 ppbv with O3-CO
slopes >0.50 mol mol−1 south of 45° N. Intense cyclones, which
were not as common in the summer, enhanced export by lofting of boundary
layer pollutants from over the US and also provided a possible mechanism for
transporting pollutants from boreal fire outflow southward to the US east
coast. Overall, for winter and summer the TES retrievals showed substantial
evidence of air pollution export to the western North Atlantic Ocean with
the most distinct differences in distribution patterns related to strong
influences of mid-latitude cyclones in winter and the Bermuda High
anticyclone in summer.